Determining and sending channel quality indicators (CQIS) for different cells

ABSTRACT

Channel quality indicators (CQIs) for each cell of a plurality of cells may be sent at a multiple of a transmission time interval (TTI). CQIs for the different cells may be in different TTIs. A timer or L 2  message may be utilized to determine when to send CQIs for different cells. CQIs for different cells may be sent over an uplink data channel in a single TTI.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.60/855,814, filed on Oct. 31, 2006, which is incorporated by referenceas if fully set forth herein.

FIELD OF INVENTION

The present invention relates to wireless communications.

BACKGROUND

The 3rd Generation Partnership Project (3GPP) is a collaborationagreement that was established in December 1998. The collaborationagreement brings together a number of telecommunications standardsbodies to produce global specifications and technical reports for a3^(rd) Generation mobile communications system. High-speed DownlinkPacket Access (HSDPA) is a feature that was introduced in Release 5 ofthe 3GPP specification. HSPDA achieves maximum spectral efficiency usingthree concepts: Adaptive Modulation and Coding (AMC), fast physicallayer retransmissions (Hybrid ARQ), and fast Node B scheduling.

FIG. 1 is a diagram of a system 100 configured to utilize HSPDA. Thesystem 100 includes a core network 102 and a radio network controller(RNC) 104 that communicates with the core network 102. A plurality ofNode Bs 106 communicate with the RNC (for clarity, only two Node Bs areshown in FIG. 1; it is understood that many more Node Bs can be incommunication with a single RNC). Each Node B 106 controls a pluralityof cells 108 (again, the number of cells 108 shown in FIG. 1 is onlyexemplary). A wireless transmit/receive unit (WTRU) 110 can communicatewith one or more of the cells 108.

AMC adapts the transmission data rate on the High Speed Downlink SharedChannel (HS-DSCH) according to the channel conditions perceived by theWTRU. Specifically, a Node B determines the best data rate, coding, andtransport block size using the following information obtained from theWTRU on the High Speed Dedicated Physical Control Channel (HS-DPCCH):

1. Channel Quality Indication (CQI), which indicates the channelconditions as monitored by the WTRU, and

2. Acknowledge/negative acknowledge (ACK/NACK) feedback used for fastretransmissions (HARQ).

Handover is the process in which a WTRU switches from one cell toanother cell without service interruption. In HSDPA, the high-speedshared channels are monitored by the WTRU in a single cell, which iscalled the “serving HS-DSCH cell”. When a handover occurs, the WTRUneeds to switch to a new serving HS-DSCH cell (the target cell/Node B)and stop communication with the old serving HS-DSCH cell (the sourcecell/Node B). This procedure is also called a serving HS-DSCH cellchange.

FIG. 2 shows a flowchart of a method 200 for performing a handoverprocedure. The WTRU continuously measures the signal strength ofneighboring cells (step 202). The WTRU compares the measured signalstrength of the neighboring cells with the strength of the signal fromthe serving cell (step 204). Once the measured signal strength on themonitored common pilot channel (CPICH) of the neighboring cell exceedsthe signal strength of the serving cell, the WTRU indicates to the RNCthat a cell change is needed (referred to as “a change of best cell”;step 206). The change of best cell is reported from the WTRU to the RNCvia an RRC MEASUREMENT REPORT event 1D. This report contains themeasured signal strength value and the cell ID. The RNC then makes thefinal decision whether a serving HS-DSCH cell change is going to occur.The handover is then executed, to switch the WTRU to the new Node B(step 208).

The new serving HS-DSCH cell needs to start downlink transmission to theWTRU at the time the channel configuration takes place (step 210). Inorder to achieve a maximum transmission rate and maximum spectralefficiency, the Node B needs to adapt to the new channel conditions asfast as possible. The channel quality conditions measured by the WTRU inthe new cell are not known by the target Node B, therefore a maximumModulation Coding Scheme (MCS) cannot be achieved right away. The Node Bhas to wait to receive a few CQI reports from the WTRU beforetransmitting at an optimal data rate.

Prior to the CQI reports being transmitted to the Node B, the targetNode B may start transmitting at a lower rate than the WTRU can support.This would waste HSDPA resources until the Node B can adapt to the newchannel conditions. Keeping in mind that the RNC performed the Node Bswitch because the downlink channel conditions are better in the newcell, the cell change could be a waste of capacity and resources.

On the other hand, prior to the appropriate number of CQI reports beingreceived by the target Node B, the target Node B may assume that the newchannel conditions are better than in the old cell and starttransmission at a higher data rate to avoid wasting HSDPA resources.However, the WTRU could be measuring unfavorable channel conditions atthe instant after handover, and might have trouble decoding the dataover the HS-DSCH. Such trouble would trigger re-transmissions and highererror rates until the Node B adapts to the new channel conditions.

Existing 3GPP Release 6 specifications do not provide support foroptimal MCS selection and scheduling for the HS-DSCH in the new servingcell after a handover occurs.

SUMMARY

A method implemented in a wireless transmit/receive unit (WTRU) fortransmitting a channel quality indication (CQI) report or othermeasurement report begins by receiving a trigger. A CQI report istransmitted to a handover target Node B until a stop condition isreached. The WTRU will stop transmitting CQI reports to the target NodeB if the stop condition is reached. A WTRU configured to perform themethod includes an antenna, a transmitter/receiver connected to theantenna, and a processor communicating with the transmitter/receiver,the processor configured to transmit the CQI report to the handovertarget Node B.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding of the invention may be had from thefollowing description, given by way of example and to be understood inconjunction with the accompanying drawings, wherein:

FIG. 1 is a diagram of a system configured to utilize HSDPA;

FIG. 2 is a flowchart of a method for performing a handover;

FIG. 3 is a diagram of an HS-DPCCH signal with two embedded CQI reports;

FIG. 4 is a diagram of another HS-DPCCH signal with two embedded CQIreports;

FIG. 5 is a flowchart of a method for transmitting a CQI report to atarget Node B; and

FIG. 6 is a diagram of a WTRU and a Node B configured to transmit andreceive CQI reports.

DETAILED DESCRIPTION

When referred to hereafter, the term “wireless transmit/receive unit(WTRU)” includes, but is not limited to, a user equipment (UE), a mobilestation, a fixed or mobile subscriber unit, a pager, a cellulartelephone, a personal digital assistant (PDA), a computer, or any othertype of user device capable of operating in a wireless environment. Whenreferred to hereafter, the term “base station” includes, but is notlimited to, a Node B, a site controller, an access point (AP), or anyother type of interfacing device capable of operating in a wirelessenvironment.

The embodiments disclosed herein relate to transmitting data over a newserving Node B after a handover procedure occurs in HSDPA. Specifically,a method is disclosed that provides the target Node B with CQI feedbackinformation required to determine the optimal transmission rate andscheduling for data at the time of cell change (i.e., prior toinitiating data transmission to the WTRU over the new HS-DSCH).

Even though the embodiments described herein relate to WCDMA systems,the concepts described are also applicable to other technologies (suchas WiMax, etc.) that support mobility and handover. Moreover, the CQIfeedback can also refer to other measurement reports used in othertechnologies.

A first embodiment makes use of the WTRU's existing uplink connection tothe Node Bs within its active set. The active set includes all of theestablished radio links with the WTRU with one or more Node Bs. Shouldthe downlink (DL) serving cell change occur within the active set, theWTRU has an existing communication context with the new Node B in theuplink (UL). In addition, if a serving cell change occurs simultaneouslywith the Active Set Update, the UL connection to the newly addedneighboring Node B can be established prior to the DL serving cellchange.

In this embodiment, the WTRU can send CQI reports to both the sourceNode B and the target Node B over the duration of the handover process.When the handover is complete, the WTRU sends CQI reports only to thenew serving HS-DSCH cell.

During the handover procedure, the WTRU monitors a number of parametersfrom the target Node B to estimate the perceived channel quality. Inthis embodiment, the WTRU reports the same CQI measurement as currentlydefined for the serving Node B.

In a second embodiment, measurement on any other downlink referencechannel can be used to derive a channel quality metric.

In a third embodiment, during a handover procedure the WTRU uses thesame high speed dedicated physical control channel (HS-DPCCH) code tosend CQI information to both the source Node B and the target Node B.The CQI report for the target Node B is appended to the CQI informationof the source Node B in the HS-DPCCH subframe.

For example, CQI 1 and CQI 2 would correspond to the CQI information ofthe source Node B and target Node B, respectively. As illustrated inFIG. 3, one HS-DPCCH subframe 300 consists of a HARQ-ACK 302, a CQI 1(target Node B report) 304, and a CQI 2 (source Node B report) 306. Theslot format can be static (e.g., a new slot format is defined and alwaysused) or dynamic where the WTRU can switch the format back and forthduring a handover procedure.

Alternatively, the feedback mechanism is based on sending theinformation on a different HS-DPCCH. When the Node B is added to theactive set, it is assigned a new HS-DPCCH code. Therefore, the Node Bshave different HS-DPCCH codes to monitor and the WTRU is aware of theallocated HS-DPCCH codes of all Node Bs within its active set.

For example, codes HS-DPCCH 1 and HS-DPCCH 2 are assigned to source NodeB and target node B, respectively. During handover, the WTRU can startsending the CQI information on code HS-DPCCH 2 to the target Node B andcontinue sending the ACK/NACK and CQI information on code HS-DPCCH 1 tothe source Node B. The CQI format within the HS-DPCCH would remain thesame.

In a fourth embodiment, the CQI pertaining to a Node B is transmittedevery other transmission time interval (TTI) or every other multiple ofTTI and the transmissions of CQIs pertaining to different Node Bs arestaggered. As shown in FIG. 4, the CQI for the target Node B (CQI(new))is in a different HS-DPCCH subframe than the CQI for the source Node B(CQI(old)). A first subframe 400 consists of HARQ-ACK 402 and the CQI(old) 404, and a second subframe 410 consists of HARQ-ACK 412 and theCQI(new) 414.

With this method, rules could be established to allow each Node B todetermine which sub-frames contain the relevant CQIs. Such rules couldbe based on the transmission timing of the HS-DPCCH relative to the SFN.Alternatively, no pre-established rule could be defined, and both NodeBs attempt to figure out which of the sub-frames pertain to their owntransmissions. Typically, the target Node B could assume that thelargest CQI pertains to its transmissions while the source Node Bconservatively assumes that the smallest CQI pertains to itstransmissions.

Alternatively, as soon as the handover occurs or at a time intervalafter the measurement report is triggered, the WTRU sends consecutiveand frequent CQI reports only to the target Node B. The frequency of theCQI reports is higher than the frequency used during normal operation.The more frequent CQI reports allows the target Node B to quickly adaptto the channel conditions. The frequency of the fast CQI reporting canbe configured by higher layers, be predetermined by the WTRU, or becontinuously transmitted on consecutive TTIs for a period of time.

In a fifth embodiment, the CQI report could be transmitted by using anyother existing or new L1 , L2 , or L3 signaling mechanism/channel.

In a sixth embodiment, the CQI reports could be mapped to an E-DCHchannel.

In a seventh embodiment, the CQI to the target Node B could be reportedusing RRC signaling, such as the measurement report message sent fromthe WTRU upon event 1D. The RNC would then forward the CQI measurementto the target Node B upon configuring the radio link to the WTRU.

FIG. 5 is a flowchart of a method 500 for transmitting a CQI report to atarget Node B, and is usable in connection with each of the CQIreporting embodiments described above. A determination is made whetherthe WTRU has received a trigger to begin transmitting CQI reports to thetarget Node B (step 502). The trigger may be based on one or anycombination of the following conditions:

1. As soon as measurement criterion event 1D is fulfilled.

2. At a time interval (Δt) after sending an event 1D measurement report,where Δt is a configurable parameter through higher layer signaling.Example values of Δt are 30 ms and 60 ms.

3. When higher layer signaling (e.g., transport/physical channel orradio bearer reconfiguration) is received by the WTRU indicating aserving cell change.

4. When the WTRU receives an RRC active set update message indicating aserving cell change. The CQI information can be sent as soon as the ULcommunication to the Node B is available.

Once the WTRU receives the trigger condition, the WTRU can begintransmitting CQI reports to the target Node B (step 504), using any ofthe embodiments described above. The WTRU can eitherperiodically/continuously transmit the CQI report or transmit the CQIreport a preconfigured number of times (e.g., once or twice). In thecase of continuous transmission, the periodicity can be configuredthrough higher layer signaling, and a mechanism is needed to stoptransmitting the CQI report to the target Node B in case the handoverdoes not take place.

A determination is made whether a stop condition has been reached (step506). The following mechanisms can be used individually or incombination to determine the stop condition:

1. A timer can be maintained at the WTRU that is started upon triggeringany of the conditions described above. The WTRU stops transmission ofCQI reports if it does not receive an indication that the handover isoccurring or will occur within the configured time.

2. Use the existing handover measurement report mechanism. Currently,the WTRU periodically sends the RRC Measurement Report message to theRNC until the RNC indicates that a handover is occurring or until apreconfigured time. The WTRU stops transmission of CQI reports when theWTRU stops sending measurement reports due to a failed handover.

3. Use existing or new L1 , L2 , or L3 signaling to indicate to the WTRUto stop transmitting the CQI report to the target Node B.

If the stop condition has not been reached (step 506), then the WTRUcontinues to transmit CQI reports to the target Node B (step 508). Ifthe stop condition has been reached, then the WTRU stops transmittingCQI reports to the target Node B (step 510) and the method terminates.

The target Node B can start decoding the CQI report from the WTRU if oneor a combination of the following conditions occur:

1. As soon as signaling is received from the RNC to reconfigure aserving radio link with this WTRU. The target Node B can use thismessage as an internal trigger to start decoding the CQI reports.

2. The Node B uses blind detection to determine whether or not a CQIreport has been sent.

FIG. 6 is a diagram of a WTRU 602 and a Node B 610 configured totransmit and receive CQI reports. The WTRU 602 includes an antenna 604,a transmitter/receiver 606 connected to the antenna 604, and a processor608 in communication with the transmitter/receiver 606. The processor608 is configured to implement the method 500 and any of the describedembodiments for transmitting a CQI report to the Node B 610.

The Node B 610 includes an antenna 612, a transmitter/receiver 614connected to the antenna 612, and a processor 616 in communication withthe transmitter/receiver 614.

Although the features and elements are described in particularcombinations, each feature or element can be used alone without theother features and elements or in various combinations with or withoutother features and elements. The methods or flow charts provided may beimplemented in a computer program, software, or firmware tangiblyembodied in a computer-readable storage medium for execution by ageneral purpose computer or a processor. Examples of computer-readablestorage mediums include a read only memory (ROM), a random access memory(RAM), a register, cache memory, semiconductor memory devices, magneticmedia such as internal hard disks and removable disks, magneto-opticalmedia, and optical media such as CD-ROM disks, and digital versatiledisks (DVDs).

Suitable processors include, by way of example, a general purposeprocessor, a special purpose processor, a conventional processor, adigital signal processor (DSP), a plurality of microprocessors, one ormore microprocessors in association with a DSP core, a controller, amicrocontroller, Application Specific Integrated Circuits (ASICs), FieldProgrammable Gate Arrays (FPGAs) circuits, any other type of integratedcircuit (IC), and/or a state machine.

A processor in association with software may be used to implement aradio frequency transceiver for use in a wireless transmit receive unit(WTRU), user equipment (UE), terminal, base station, radio networkcontroller (RNC), or any host computer. The WTRU may be used inconjunction with modules, implemented in hardware and/or software, suchas a camera, a video camera module, a videophone, a speakerphone, avibration device, a speaker, a microphone, a television transceiver, ahands free headset, a keyboard, a Bluetooth® module, a frequencymodulated (FM) radio unit, a liquid crystal display (LCD) display unit,an organic light-emitting diode (OLED) display unit, a digital musicplayer, a media player, a video game player module, an Internet browser,and/or any wireless local area network (WLAN) module.

What is claimed is:
 1. A wireless transmit/receive unit (WTRU)comprising: a processor configured to determine a plurality of channelquality indicators (CQIs) from measurements of downlink transmissionsfrom different cells; the processor and a transmitter are configured totransmit, to a network node, control information in transmission timeintervals (TTIs) on a physical control channel, wherein the controlinformation includes the plurality of CQIs; wherein CQIs for a firstcell of the different cells are transmitted at a multiple of a TTI andCQIs for a second cell of the different cells are not transmitted inTTIs having CQIs of the first cell; wherein a timer is configured inrelation to a control signal received by the WTRU; wherein, in responseto expiration of the timer for the first cell, the transmission of thecontrol information including the plurality of CQIs is ceased for thefirst cell and transmission of CQIs continue for the second cell;wherein the transmission of the CQIs for the second cell is ceased inresponse to a received layer 2 (L2) message while transmission of CQIsfor at least one other of the different cells continues; and thetransmitter is further configured to transmit non-ceased CQIs for the atleast one other of the different cells over an uplink data channel in asingle TTI.
 2. The WTRU of claim 1, wherein the processor and thetransmitter are further configured to switch between sending controlinformation indicating the plurality of CQIs and sending controlinformation indicating a single CQI.
 3. The WTRU of claim 1, wherein theplurality of CQIs are associated with different Node Bs.
 4. The WTRU ofclaim 1, wherein the network node is a Node B.
 5. The WTRU of claim 1,wherein the downlink transmissions are received using a high speeddownlink shared channel (HS-DSCH).
 6. The WTRU of claim 1, wherein thephysical control channel is a High Speed Dedicated Physical ControlChannel (HS-DPCCH).
 7. The WTRU of claim 1, wherein the different cellsare High-speed Downlink Packet Access (HSDPA) serving cells.
 8. A methodperformed by a wireless transmit/receive unit (WTRU), the methodcomprising: determining, by the WTRU, a plurality of channel qualityindicators (CQIs) from measurements of downlink transmissions fromdifferent cells; transmitting, by the WTRU to a network node, controlinformation in transmission time intervals (TTIs) on a physical controlchannel, wherein the control information includes the plurality of CQIs;wherein CQIs for a first cell of the different cells are transmitted ata multiple of a TTI and CQIs for a second cell of the different cellsare not transmitted in TTIs with CQIs of the first cell; wherein a timeris configured in relation to a control signal received by the WTRU;wherein, in response to expiration of the timer for the first cell, thetransmission of the control information including the plurality of CQIsis ceased for the first cell and transmission of CQIs continue for thesecond cell; wherein the transmission of the CQIs for the second cell isceased in response to a received layer 2 (L2) message while transmissionof CQIs for at least one other of the different cells continues; andtransmitting, by a transmitter of the WTRU, non-ceased CQIs for the atleast one other of the different cells over an uplink data channel in asingle TTI.
 9. The method of claim 8 further comprising: switching, bythe WTRU, between sending control information indicating the pluralityof CQIs and sending control information indicating a single CQI.
 10. Themethod of claim 8, wherein the plurality of CQIs are associated withdifferent Node Bs.
 11. The method of claim 8, wherein the network nodeis a Node B.
 12. The method of claim 8, wherein the downlinktransmissions are received using a high speed downlink shared channel(HS-DSCH).
 13. The method of claim 8, wherein the physical controlchannel is a High Speed Dedicated Physical Control Channel (HS-DPCCH).14. The method of claim 8, wherein the different cells are High-speedDownlink Packet Access (HSDPA) serving cells.